Project Summary: As an obligate intracellular parasite HIV, like all viruses, relies on host-encoded factors to complete its life cycle inside the host cell. However, the virus must also evade recognition by specialized host factors that have evolved specifically to defend cells against viral invasion. Some of the antiviral genes are part of an Interferon-induced transcriptional program that is deployed by the host on sensing of a viral invader. A comprehensive description of host genes that block primate lentiviruses from successfully infecting human cells has evaded characterization with current methodologies. In Aim 1 we will describe the mechanism of inhibition of HIV-1 and related primate Simian Immunodeficiency Virus (SIV) variants by TRIM34, a TRIM5 paralog we have discovered to specifically target HIV-1 capsid variants and SIVs. In Aim 2 we will explore the role of TRIM34 as a broadly acting antiviral gene in primates as well as the potential role of TRIM34 in contributing to limiting the evolution of HIV-1 infections within the host. In Aim 3 we will perform a whole-genome HIV-CRISPR screening approach to find the Interferon-Stimulated Genes (ISGs) that inhibit HIV-1 capsid mutants. In addition to defining a novel HIV restriction by TRIM34 in human cells, this work has the potential to discover novel host antiviral genes that limit SIV and HIV strains from replicating in human cells. Follow-up studies will be focused on furthering our understanding the mechanism of action of genes of interest as well as mechanisms of viral antagonism or escape. Ultimately, manipulation of these factors could be important for approaches aimed at achieving a functional HIV cure.